Archive for the ‘Equipment’ Category

I’m currently experimenting with measuring grass minimum temperature. The grass minimum is defined as the temperature recorded in open air ground on short turf, with the bulb of the thermometer just in contact with the tips of the blades of grass. It is also described as the temperature at 5cm or 2 inches above the ground. The difference between the air temperature typically measured around 4 to 5 feet above ground and the grass minimum can be substantial on clear nights with little wind and strong radiational cooling. When I have enough data to plot, I’ll post the graphs. I’m using a Davis wireless temperature station for the grass minimum temperature. Since it is directly exposed to the sun, the daytime readings have little use and could be cause for concern if I posted, frequently reporting over 100º this summer! The grass minimum is the lowest temperature recorded between sunrise and 0900.

Grass Minimum Sensor

I have opted to just post the recorded minimum from the sensor on the garden weather page of my website available here.

I’ve just added 2 new measurements to the Goose Lake Weather station, soil temperature and soil moisture. Readings for these 2 parameters are now available at 4, 12, 24 and 36 inch depths. The data is currently available from the Daily Stats link. I hope this data will yield information useful to gardeners like myself. It will also help to estimate the frost depth in the winter and early spring. I also hope to install a frost tube in the near future but more on that later.

Watermark Soil Moisture Sensor

The soil moisture readings utilize a Watermark brand sensor. The Watermark sensor (granular matrix sensor) is an indirect, calibrated method of measuring soil water. It is an electrical resistance type sensor, which converts the electrical resistance reading to a calibrated reading of Centibars (or kPa) of soil water tension. It does take some time (weeks to months) for the soil moisture readings to stabilize to the surrounding soil.

Centibar Reading Soil Condition

0-10

Saturated Soil. Occurs for a day or two after irrigation.

10-20

Soil is adequately wet (except coarse sands which are drying
out at this range)

30-60

Usual range to irrigate or water (except heavy clay soils).
Irrigate at the upper end of this range in cool humid climates
and with higher water-holding capacity soils.

You may have noticed that my rainfall readings did not update in real-time while we received rainfall during this last event. I’ve covered the gauge with a cap because the gauge is not heated. When it snows, rain will collect in the gauge and melt when it warms. The melt could be several days after the snowfall. So to prevent this, I’ve covered the gauge. I do take rainfall readings manually each morning around 6 am. If snow falls, the manual gauge will collect the snow. I’ll then bring in the gauge to melt the snow to determine the liquid water equivalent. I’ll then add this to the accumulated monthly and yearly totals that you see on the web page.

Upgraded the weather PC this weekend and retired the old P4. It was maxed out at 512RAM and the continuous data collection and now web cam capture was bringing it to a crawl. A new UPS system was also installed.